The die casting industry is an old and well-established industry which has, in recent years, experienced growth into an ever-increasing range of die cast products. This growth, however, is believed to have been severely restricted by the large number of complex and seemingly interrelated problems which have long been experienced in this industry. Many of these problems have never been adequately solved and, at best, are normally attacked solely on an individualized trial-and-error basis. This results in this industry operating at substantially less than maximum efficiency, which thereby greatly increases the cost of products produced by this process, and also severely restricts the applicability of this process to different products.
One area which has long presented a problem in the die casting industry relates to the die. For example, the proper filling of the die has long been a serious problem, and monitoring the filling of the die is basically a trial-and-error procedure which, when solved, is then repetitively followed during production. The die area has also presented a serious problem with respect to proper determination of the minimum time required for solidification of the metal in the die so as to ensure that the die can be separated within the shortest possible time, thereby permitting maximum rate of production. At the same time, it is necessary to avoid separation prior to solidification of the metal, since this not only destroys the cast part but also often causes a freeze-up of the machine which requires substantial machine maintenance prior to placing the machine in condition for further operation.
Another area which has long plagued the die casting industry relates to the die casting apparatus and specifically the shot sleeve assembly. The shot sleeve assembly has, for the most part, been substantially ignored by the die casting industry, even though this assembly has long presented a serious problem with respect to wear, maintenace and replacement. Since problems relating to the shot sleeve assembly are normally not caused by a single factor or condition, but rather are the result of numerous interrelated complex factors, the industry has accordingly accepted these problems and has thus accepted a performance level substantially less than optimum. For example, the die casting industry normally accepts these problems and solves same by tolerating substantially short life in these assemblies, which requires replacing or reworking these assemblies on a frequent basis in order to keep the die casting machine in operation. While various attempts have been made at improving the shot sleeve assembly, most of these attempts have concentrated on trying to solve one specific problem or factor as it relates to the overall assembly. Because of this, these attempts have resulted in structures which have been far less than satisfactory and have not provided a complete solution to the problem, since these attempts have failed to take into account the numerous interrelated and rather complex factors which influence the design of a successful shot sleeve assembly.
The specific problems experienced with the shot sleeve assembly, which problems have existed for many years, are briefly summarized as follows:
1. Cracking: Since a substantial quantity of extremely hot molten metal is intermittently deposited into the shot sleeve assembly, this causes substantial heating of the sleeve, which heating is highly nonuniform both circumferentially and radially of the sleeve due to (1) the irregular positioning of the material within the sleeve and (2) the manner in which the material is deposited in the sleeve and then pushed into the die cavity. This results in severe temperature gradients within the sleeve, which in turn induces severe thermal stresses. These stresses can result in severe thermal cacking of the sleeve, which cracking often takes the form of surface cracks or, in the extreme, causes a crack throughout the radial wall of the sleeve which may extend partially or totally through the axial extent thereof. This cracking obviously destroys the sleeve, which destruction often takes place after a relatively small number of cycles.
2. Sleeve wear: The sleeve often experiences substantial wear in the internal surface thereof directly opposite the pour hole. This wear occurs due to an erroding of the sleeve material due to the thermal tempering and resulting abrasion of the sleeve directly opposite the pour hole. This results in an enlargement of the interior of the sleeve, which thereby requires a reworking or reboring of the sleeve. This changes the volume of the sleeve and necessitates the provision of a new enlarged tip member. This also effects the volume of the chamber and the quantity of molten metal being injected into the die cavity.
3. Tip wear: The plunger tip which is slidable within the sleeve also experiences substantial wear and requires frequent replacement, normally at intervals even more frequent than the sleeve. Tip wear is compounded by the wear of the sleeve, as discussed above, which often permits metal deposits to collect within the sleeve. These metal deposits abrasively score the surface of the tip, particularly the leading edge thereof. The wear of the tip, or any significant increase in clearance between the tip and the sleeve, also creates a potentially dangerous operational condition in that the hot molten metal can blow back around the tip and be discharged into the surrounding environment, thereby creating a hazard to the operating personnel.
4. Distortion: The thermal stresses induced in the sleeve by the hot molten metal, as discussed above, also result in substantial distortion of the sleeve. This distortion is of two types, the first being circumferential in that it causes the sleeve to assume an out-of-round shape, and the second being axial in that the sleeve assumes a bowed or "banana" shape. This greatly increases the wear of the sleeve, and particularly the tip since it is normally constructed of a softer material such as berylliumcopper. This also seriously effects the desired clearance between the tip and the sleeve, which increases the possibility of material blow-by.
5. Replacement: The replacement of the sleeve, as required by excessive wear or breakage, is extremely laborious and time-consuming. Many sleeves are mounted on the die platen by being inserted into the platen from the die side. This requires removal of the die prior to gaining access to the sleeve. Since removal of the die is both laborious and time-consuming, and normally involves the utilization of a fork lift truck and requires anywhere from several hours to several days, this replacement operation is obviously very inefficient and costly. Further, the sleeve often seizes within the platen due to thermal distortion. This thus makes removal of the damaged sleeve extremely difficult.
6. Clearance: The clearance between the interior bore of the sleeve and the cylindrical tip member slidably disposed therein is critical if efficient operation of the die casting machine is desired for long periods of time. This clearance must be maintained at a minimum to prevent the blow-by of molten metal past the tip member, which is obviously undesirable as explained above. In addition, if this clearance becomes excessive, then the molten metal causes rapid wear and errosion of the tip member, which not only further increases the clearance but also greatly shortens the life of the tip member. At the same time, suitable clearances must be maintained to permit free sliding movement of the tip member. Due to the substantial temperature changes experienced by the sleeve, and the nonuniform thermal distortions which occur therein, maintaining a proper clearance between the sleeve and the tip member has, heretofor, been substantially impossible. The maintaining of a desired clearance has been further complicated by the fact that, for many years, it has been a conventional practice to cool the tip member by continuously circulating a liquid coolant (such as water) therethrough. While this maintains the tip member at a lower and more uniform temperature, nevertheless none of the prior structures have been able to provide a similar optimum uniform cooling of the sleeve. Thus, maintaining the desired substantially uniform clearance between the sleeve and the tip member has been substantially impossible.
While various attempts have been made to improve the design of the shot sleeve assembly, nevertheless most of these prior attempts have concentrated on only one or two of the specific problems which have been explained above. These prior attempts, while possibly slightly improving the shot sleeve assembly, have nevertheless failed to greatly improve this structure since they have failed to take into account the overall interrelationship of the above-mentioned numerous problems.
For example, U.S. Pat. No. 3,209,416 discloses a shot sleeve assembly for a die casting machine which is provided with an annular groove therearound for receiving a coolant. The shot sleeve is of a one-piece structure and the annular coolant groove is closed by a wall formed on the lower die platen. This shot sleeve assembly, however, fails to solve the numerous problems mentioned above since the coolant is concentrated solely within the small annular groove which is located adjacent the middle of the sleeve. There is no cooling of the end portions of the sleeve, so that the cooling is thus very nonuniform in the axial direction of the sleeve. This accordingly results in substantial thermal gradients and stresses in the sleeve which induce nonuniform distortion, whereby the desired clearance between the tip member and the sleeve is accordingly destroyed. At the same time, this one-piece cooled sleeve is subject to substantial thermal cracking since the sleeve is directly contacted not only on the inside thereof by the hot molten metal, but is also directly contacted on the outside thereof by the coolant. This direct contact of the same one-piece sleeve by both the molten metal and the coolant results in extreme thermal gradients radially through the wall of the sleeve, which makes the sleeve very prone to cracking. This type of cooling arrangement is also difficult to control with respect to the desired amount of cooling since, by permitting the coolant to directly contact the sleeve containing the molten metal, this arrangement permits extracting too much heat from the molten metal, which thereby requires that the molten metal be deposited into the sleeve at a higher temperature, or in the alternative results in excessive cooling of the molten metal so that the desired fluidity thereof is reduced resulting in improper filling of the die cavity. This sleeve is also subject to the problem of seizing within the platen since the end portions can still thermally expand through undesired amounts and thermally distort a sufficient amount to seize the die platen.
U.S. Pat. No. 3,516,480 discloses another attempt to overcome the above problems by providing a cooled shot sleeve assembly. In the structure of this patent, the assembly is formed by utilizing an outer cooled sleeve having an inner sleeve (or liner) snugly fit therein. The outer sleeve has a narrow cooling insert extending axially thereof adjacent the very bottom of the outer sleeve. The shot sleeve assembly of this patent, however, also fails to provide an effective solution to the numerous problems which have been outlined above. To begin with, the cooling in this sleeve assembly is concentrated in a narrow axially extending region along the bottom of the outer sleeve, so that there is not proper cooling circumferentially around the sleeve. This thus results in the heat being extracted solely adjacent the bottom of the sleeve assembly, whereby severe thermal gradients are set up circumferentially of the sleeve. This subjects the sleeve assembly to severe distortions which cause it to assume an axially bowed and/or an out-of-round shape. This makes the inner sleeve or liner subject to cracking, particularly splitting in the longitudinal direction thereof due to the concentration of the cooling along the narrow axially extending region. Since the outer sleeve is also subject to substantial expansion and distortion, it is also subject to splitting or at least separating from the cooling insert. This sleeve arrangement also results in the clearance between the liner and the plunger tip being substantially increased in a nonuniform manner due to the nonuniform expansion of the sleeve assembly, thereby destroying the desired clearance between the tip and the liner, which in turn greatly increases the rate of tip wear.
U.S. Pat. No. 3,685,572 discloses a modified shot sleeve assembly which is of a multi-part construction provided with limited clearances between portions of some parts to permit limited radial expansion therebetween. While the shot sleeve assembly of this patent does attempt to control the thermal distortion of the shot sleeve assembly, nevertheless the control achieved by this structure is far less than that required in order to result in optimum performance and life of the shot sleeve assembly and the associated tip member. For example, the shot sleeve assembly of this patent discloses that the clearances between the inner and outer sleeves need extend over only part of the axial length of the sleeves. This, however, is totally undesirable since these sleeves are still in snug engagement with one another at the opposite ends whereby undesired thermal stresses and hence nonuniform thermal distortions still occur. This patent thus does not recognize the need to provide such clearances axially throughout the complete length of the sleeve in order to provide optimum control over the thermal stresses and distortions of the sleeve assembly. Absent this optimum control, the desired uniform clearance between the tip and the liner is accordingly not maintained throughout the axial length of the assembly. In addition, the shot sleeve assembly of this patent does not recognize the need for cooling the liner assembly, and hence this assembly results in undesired heating which causes excessive thermal stresses and distortions of the sleeve assembly. In addition, this shot sleeve assembly utilizes an outer casing which must be positioned in the die platen from the die side thereof, and in fact this outer casing is bolted directly to one of the dies. Thus, any seizing or cracking of the shot sleeve assembly requires a complete shutdown of the machine and removal of the dies in order to permit removal of the outer casing. Further, the shot sleeve assembly of this patent is formed from a large number of different sleeve members, and in fact utilizes several different sleeve members in coaxial alignment with one another. Due to the different thermal stresses and distortions throughout the axial length of the sleeve assembly, the use of these different axially aligned sleeve members can compound the wear of the tip member due to the different expansions experienced by the different liner members, resulting in undesired edges or corners along the sleeve bore. These mating corners or edges are also subject to collecting metal deposits which also greatly accelerates the tip wear. Thus, the shot sleeve assembled of this patent does not take into account the numerous complex and interrelated factors which must be considered in designing a shot sleeve assembly to effectively overcome or at least compensate for the numerous problems mentioned above.
At the present time, most die casting machines are totally or at least partially manually controlled, and most often utilize either manual filling of the shot sleeve with molten metal, or utilize ladling apparatus which is manually controlled. Thus, most die casting machines thus operate at less than maximum capacity since they are limited with respect to the manual rate at which the operation can be carried out. Nevertheless, even though this rate of production is limited due to the control conditions which are effected by manual manipulations, nevertheless the above-mentioned problems are still encountered repetitively and at a rather frequent rate, which thus results in the production capacity of the machine being still further impaired. At the present time, however, the use of automatic ladling equipment is becoming more common and this equipment does, theoretically, permit the production rate to be substantially increased. However, any such increase in the production rate by use of automatic ladling equipment causes the heating of the shot sleeve assembly to become even more severe, so that the above-mentioned problems become even more pronounced. Thus, mere utilization of automatic ladling equipment or the like has not had a significant impact on the efficient utilization of the die casting machine since it merely accelerates the failure of the shot sleeve assembly due to one or more of the above-mentioned problems.
Accordingly, it is a primary object of the present invention to provide an improved shot sleeve assembly for a die casting machine, which shot sleeve assembly attempts to take into account the many interrelated factors which effect this assembly so as to at least partially solve, or at least improve upon, most of the many different problems discussed above. Further, the shot sleeve assembly of this invention represents a substantial improvement over the structures disclosed in the above-mentioned patents, by eliminating or at least substantially minimizing the disadvantages associated with these prior structures.
More specifically, it is an object of this invention to provide:
1. An improved shot sleeve assembly which includes an improved cooling system associated therewith for permitting increased life of the shot sleeve and minimization of thermally induced failures such as cracking and the like.
2. A shot sleeve assembly, as aforesaid, which provides for more uniform cooling of the shot sleeve assembly to thereby make same more compatible with the cooled plunger tip, whereby a more uniform and controlled clearance is maintained between the tip and the shot sleeve during operation.
3. A shot sleeve assembly, as aforesaid, which provides for more controlled cooling of the shot sleeve assembly to prevent, or substantially minimize, thermally induced distortion of the shot sleeve assembly, both circumferentially and axially, thereby minimizing both thermal cracking and wear.
4. A shot sleeve assembly, as aforesaid, which provides an inner sleeve or liner for receiving the molten metal and an outer sleeve through which circulates the coolant, whereby the thermal gradients within the inner sleeve can be minimized and at the same time provide for more uniform extraction of heat from the inner sleeve both circumferentially and axially thereof.
5. A shot sleeve assembly, as aforesaid, which permits the inner sleeve to be constructed of a hardened and tempered steel capable of withstanding the hot molten metal, while at the same time permitting the outer sleeve to be of a milder and more tempered steel capable of being readily machined so as to accommodate the necessary cooling passages therein.
6. A shot sleeve assembly, as aforesaid, which due to its concentric sleeve arrangement provides for more controlled extraction of heat from the inner sleeve to thereby avoid excessive cooling of the molten metal, while at the same time permitting the molten metal to be supplied to the sleeve at a minimum temperature to avoid or minimize the tempering of the inner sleeve opposite the pour hole, whereby errosion of the material opposite the pour hole is likewise minimized.
7. A shot sleeve assembly, as aforesaid, which increases the life of both the inner sleeve and the tip member several times in contrast to prior structures, and at the same time provides a more uniform and controlled clearance between the tip member and the inner sleeve to minimize the possibility of material blow-by and also minimize the possibility of air entering into the molten metal and causing porous castings.
8. A shot sleeve assembly, as aforesaid, which greatly facilitates maintenance and/or replacement of the shot sleeve by permitting the inner sleeve to be removed and/or replaced on the machine without requiring removal of the die assembly.
9. A shot sleeve assembly, as aforesaid, which permits the inner sleeve to be slidably removed from the outer cooling sleeve without requiring demounting of the cooling sleeve from the platen, and which permits the inner shot sleeve to be slidably removed from the back or rearward side of the platen.
10. A shot sleeve assembly, as aforesaid, wherein a slight clearance exists between the inner and outer sleeves when they are substantially at the same temperature, such as ambient temperature, to permit (1) the inner sleeve to be easily slidably removed from the outer sleeve, (2) the minimization of thermal stresses and distortions in both of the sleeves due to the permitted thermal expansion of the inner sleeve prior to engagement with the outer sleeve and (3) the more uniform transfer of heat from the inner sleeve to the outer sleeve due to the uniformity of engagement therebetween as caused by the initial thermal expansion of the inner sleeve.
11. A shot sleeve assembly, as aforesaid, which simplifies and greatly minimizes the maintenance and repair of the shot sleeve, which greatly minimizes the shutdown time of the die casting machine, and which greatly facilitates the interchangability of the inner sleeve.
12. A shot sleeve assembly, as aforesaid, which is readily adaptable for use in either horizontal or vertical die casting machines.
13. A shot sleeve assembly, as aforesaid, which is highly adaptable for use on a die casting machine used with automatic ladling equipment or the like to permit the machine to be operated at an increased rate per unit time, such as an hourly rate, while at the same time permitting the machine to operate for longer priods of time without requiring shutdown for maintenance and/or repair of the shot sleeve assembly.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this type upon reading the following specification and inspecting the accompanying drawings.